feat(usage): add auto-refresh interval for usage queries

New Features:
- Users can configure auto-query interval in "Configure Usage Query" dialog
- Interval in minutes (0 = disabled, recommend 5-60 minutes)
- Auto-query only enabled for currently active provider
- Display last query timestamp in relative time format (e.g., "5 min ago")
- Execute first query immediately when enabled, then repeat at intervals

Technical Implementation:
- Backend: Add auto_query_interval field to UsageScript struct
- Frontend: Create useAutoUsageQuery Hook to manage timers and query state
- UI: Add auto-query interval input field in UsageScriptModal
- Integration: Display auto-query results and timestamp in UsageFooter
- i18n: Add Chinese and English translations

UX Improvements:
- Minimum interval protection (1 minute) to prevent API abuse
- Auto-cleanup timers on component unmount
- Silent failure handling for auto-queries, non-intrusive to users
- Prioritize auto-query results, fallback to manual query results
- Timestamp display positioned next to refresh button for better clarity

src/i18n/locales/zh.json

@@ -338,7 +338,11 @@
     "invalid": "已失效",
     "total": "总：",
     "used": "使用：",
-    "remaining": "剩余："
+    "remaining": "剩余：",
+    "justNow": "刚刚",
+    "minutesAgo": "{{count}} 分钟前",
+    "hoursAgo": "{{count}} 小时前",
+    "daysAgo": "{{count}} 天前"
   },
   "usageScript": {
     "title": "配置用量查询",
@@ -355,6 +359,8 @@
     "queryFailedMessage": "查询失败",
     "queryScript": "查询脚本（JavaScript）",
     "timeoutSeconds": "超时时间（秒）",
+    "autoQueryInterval": "自动查询间隔（分钟）",
+    "autoQueryIntervalHint": "0 表示不自动查询，建议设置 5-60 分钟",
     "scriptHelp": "脚本编写说明：",
     "configFormat": "配置格式：",
     "commentOptional": "可选",